1. Field
The present invention relates to electronic devices for analog-to-digital conversion, more specifically to a sigma-delta analog-to-digital converter for use with multiplexed input channels.
2. Description of the Related Art
Micro-Electro-Mechanical Systems or MEMS can be defined as micro-scale mechanical and electro-mechanical systems where at least some elements have a mechanical functionality. MEMS structures can be applied to quickly and accurately detect very small changes in physical properties.
The vast majority of electronic devices today use the MEMS sensors to detect some specific physical phenomenon. The measured signals describing these phenomena are usually in the analog domain. Since signal processing and storage are effective to perform in the digital domain, the signals have to be converted to the digital domain using Analog-to-Digital Converters (ADC).
One method for encoding analog signals to digital signals is delta-sigma-conversion. In the delta-sigma-conversion, an analog signal is first encoded with sigma-delta modulation and digital filtering is used to form a higher-resolution digital output. Delta-sigma analog-to-digital converters are usually used with modern ASIC technologies, since their topology does not require perfect matching of high performance passive components, a higher sampling frequency can be used to improve the resolution, and required decimation filtering is effectively implemented with modern ASIC technologies.
In multi signal processing systems there is a need to convert many signals to the digital domain. The challenge with delta-sigma analog-to-digital converters is that they need a considerable time to settle between input signals, and this settling causes delay to the switching between signal channels. Due to this, when high data resolution has been required, parallel delta-sigma modulators have been used. This approach is, however, chip area consuming.
Another conventional option is to reduce the delay by multiplying the number of digital filters and switching the output signal of the delta-sigma modulator between them. The settling time of the modulator can be taken into account by discarding some samples of the delta-sigma-modulator. This facilitates area reduction by multiplexing but reduces the data rate and signal bandwidth of the conversion.